1. Field of the Invention
The present invention relates to an optical fiber ribbon assembly, and particularly to an optical fiber ribbon assembly with strain relief integrated therein.
2. Description of Related Art
Optical fibers are now used in a variety of telecommunication applications because of small physical size and high bandwidth capacity. An optical fiber cable typically contains a number of individual optical fibers. The optical fibers can be contained in the cable in a variety of configurations, such as loose-tube cables, tight-buffered cables, or optical fiber ribbons.
It is not uncommon that an optical fiber cable containing an optical fiber or optical fibers undergoes rough handling or is exposed to a physical environment that stresses the fiber or fibers within the cable. For example, an optical fiber contained in an optical fiber cable can experience stress and strain when the cable is bended or stretched during winding on a reel for purposes of storage. An optical fiber cable pinched between other cable components may subject to mechanical stress due to difference between the coefficients of thermal expansion for the optical fiber and the other components, such as a tube of the optical fiber cable containing the fiber or a protective layer of an optical fiber ribbon cable.
A variety of techniques have been developed to hold and protect individual fibers from damage. For example, fibers are frequently encased in a jacket or other protective material. In addition, individual fibers are often grouped together to provide a cable capable of carrying increased amounts of information.
Cylindrical optical fiber cables usually employ additional protective layers to release stochastic strain or stress exerted thereon. These protective layers commonly include buffer tubes/layers, strength members, filler members in loose-tube type cables, and thick jackets made of PVC or other proper materials.
However, in the case of ribbon type optical fiber cables, some of the more ordinary protective means, such as filler members, used in the cylindrical optical fiber cables become unfeasible. Instead, other protective design using elements such as buffers or strength members, can be applied around individually optical fibers contained in a ribbon cable. Although polyvinyl chloride (PVC) protective layers can also be used to alleviate strain or stress put on the ribbon, it is often not enough to protect the ribbon from stochastic overloaded tension exerted thereon during installation or occasions thereafter.
Individual optical fibers have been woven into sheets, providing a workable solution to the above-discussed problems. For example, as disclosed in U.S. Pat. Nos. 5,524,679, 5,469,895, 5,280,558 and 5,256,468, optical fibers are woven into a supporting structure. Once completed, the woven, grid-like mat can be coated with various types of protective material, such as an elastomer or a rubber epoxy, to form a flexible sheet with the optical fibers embedded therein. Alternatively, the structure can be coated or embedded in a rigid material, such as epoxy, to form a hard or rigid grid-like structure.
Although such flexible or rigid grid-like mat structures can achieve good tensile resistance, they unavoidably result in a highly complicated manufacture with attendant high costs.
Another related prior art for solving the problem discussed above is disclosed in U.S. Pat. No. 4,679,897 as shown in FIG. 5. An optical fiber ribbon cable combination 1 includes a pair of plastic tapes 14, a ribbon 10 consisting of a plurality of optical fibers 15, and a pair of plastic insulated copper conductors 12. The ribbon 10 is disposed between the pair of conductors 12 and the conductors 12 extend lengthwise of the tape along with the ribbon 10. The ribbon 10 and the conductors 12 are sandwiched between the pair of tapes 14. The ribbon 10 is loosely housed within an elongate compartment defined by the conductors 12 and the tapes 14. When a tensile force is applied to the cable 1, the conductors 12 and the tape 14 help carry the tensile load, sparing the ribbon 10 from carrying all the whole tensile load.
However, the conductors 12 can be easily disconnected from the tape 14 under the tensile force applied thereon since the conductors 12 are only attached to the pair of tapes 14 by fusion bonding. Furthermore, although the ribbon 10 is loosely housed in the compartment between the conductors 12, it is still possible for it to be subjected to bear the transverse tensile force applied on the cable 1, especially when the cable 1 is transversely bent and the conductors 12 have nearly between detached from the tape 14.
An object of the present invention is to provide an optical fiber ribbon which can be tensile loaded without damage to optic fibers therein and which can be manufactured at low cost.
Another object of the present invention is to provide an optical fiber ribbon having strain relief structures for mitigating the tensile force applied to the optic fibers.
In accordance with one aspect of the present invention, an optical fiber ribbon assembly comprises: a plurality of aligned optical fibers; a strain relief structure aligned with the fibers, and a protective layer integrally bonding the fibers and the strain relief structure together. The strain relief structure has at least a pair of strength members disposed on opposite sides of the aligned fibers and extending lengthwise along the ribbon assembly. The strength members can be copper conductors or can be made of KEVLAR.